This invention concerns air structures - that is to say structures the major boundary walls of which are defined by flexible material that is at least substantially impermeable to air and intended to be supported and/or stiffened into a desired configuration by the application of a pressure differential to the respective surfaces thereof. A hot-air balloon is an example of such a structure but the principles involved have been applied or proposed for application to a wide variety of constructs, such as stadia and like arenas, temporary buildings and enclosures for, e.g., exhibition purposes, greenhouses and so on.
With certain exceptions, most air structures hitherto constructed or proposed have relied upon inflation of their contained volume or of some part thereof to establish the required pressure differential to support and/or stiffen the flexible walls into the desired configuration. This inflation has in general been accomplished by the use of mechanical devices such as fans and blowers driven by energy-consuming motors so that although the structure may have a low energy content in the materials of its construction, as well as the advantages of light weight and ease of construction and erection, its continued existence in an erected condition involves the continuing expenditure of energy.
An object of the present invention is therefore to provide an air structure the erection and maintenance of which is at least partly accomplished by the utilisation of energy derived from its surroundings, for instance solar radiation energy.
The use of solar radiation energy for inflation of an air structure has been proposed hitherto but such proposals as have been tested have exhibited unsatisfactory characteristics, mainly as a result of their being based upon constructional principals applicable to structures intended to be inflated and maintained by the continuous application of internal positive pressure by mechanical devices. For the efficient utilisation of solar radiation, the direct conversion of such radiation to longer-wave energy must take place within the confines of the structure and accomplish direct heating of the air therewith in order to achieve the required pressure differential for satisfactory inflation of the structure. Such design principles therefore imply the utilisation of wall-forming components that are suitably transparent to the solar radiation.
In general it has not been found possible, hitherto, to obtain an adequate pressure differential across the walls of such a structure, inflated by the use of solar radiation energy, to make the structure sufficiently rigid to resist deformation under wind loads. Moreover, in common with mechanically-inflated structures, the existence of a positive pressure within the structure tends to supplement the aerodynamic lift forces that are applied to the structure by winds blowing thereover. Accordingly, structures such as hitherto proposed to be maintained by utilisation of solar energy would in general be viable only in relatively still air conditions.